Efficient use of water under Mediterranean conditions: Agronomic tools

Abstract

The efficient use of water is crucial under Mediterranean conditions, due to the development of water stress during late spring and summer. However, an astonishing intra-annual variability of rainfall makes any solution very complex. Production techniques need to be adapted to this variability, thereby increasing the availability of and the efficiency with which crops utilize water. Tillage plays a major role in both aspects. No-till reduces runoff and therefore increases the amount of water stored in the soil, particularly in dry years. If crop residues are maintained on the soil surface, No-Till reduces the water lost by direct evaporation, although the benefits depend on the frequency of rain or irrigation events. The volume of soil porosity available for water storage is also affected by tillage, although information in the literature is somewhat contradictory. However, if organic matter increases under conservation agriculture the water storage capacity of the soil tends to increase. Crop rooting depth also plays an important role on the water available to the crop and for depths greater than tillage the presence of continuous bi-pores might be crucial for the rapid elongation of the root system into deeper soil layers. This aspect might be particularly important in Luvisols where the growth of the roots in the B horizon can be enhanced by long term No-Till. Under these circumstances No-Till improves saturated hydraulic conductivity of the soil that, together with greater soil cohesion, improves the soil bearing capacity, contributing for timelier field operations, such as seeding, fertilizer and herbicide applications, that can improve the water use efficiency by the crop. The effect of the seeding time on crop yield depends on the crop and the precipitation of the year. The best seeding time for winter crops is from mid-November to mid-December, for seasons when rainfall at least equals the annual average value but October sowing is better in drier than average years. For rainfed spring crops the best seeding time is the beginning of February, irrespectively of the rainfall. The amount and timing of nitrogen application to winter crops depends on the amount of rainfall. In wet winters a top-dressing in January is crucial, but timing is depended on the trafficability of the soil. This aspect is also important for early application post-emergence herbicides. Both applications can be decisive for good cereal yields in wet years and therefore for water use efficiency. Crop rotation also plays a role in the water available in the soil. Rainfed, long-season spring crops like sunflower depletes the soil water by the end of summer and impair the yield of the next crop in a dry year.